We have demonstrated that adenosine deaminase (ADase) binding proteins can be extracted from membranes derived from human placenta. We propose that these proteins function to juxtapose ADase to the nucleoside transport system. To test this hypothesis we plan: 1) To obtain biochemical evidence for a membrane macromolecular complex of ADase, binding protein and the nucleoside transport system. Further support for an interaction with 5'-nucleotidase will be sought. Specific approaches will include covalent crosslinking followed by SDS gel electrophoresis, purification of a functional complex by specific affinity chromatography, and incorporation of a functional unit containing these components into a proteoliposome. A subcellular distribution of the binding protein by isolation of specific organelles will be performed for further documentation of a plasma membrane origin; 2) to determine structure-function relations of the purified binding proteins by studying the binding capabilities of non-identical subunits separated by solvent perturbation. We will seek to establish whether any of the polypeptide chains are amphipathic, containing hydrophobic and hydrophilic segments for binding and biological activities, respectively; and 3) to elucidate characteristics of the ADase-binding protein interaction, including evidence for a dynamic equilibrium regulated by metabolites, the effect of binding on catalytic properties, and the functional significance of electrophoretic variants and carbohydrate moieties. We will compare physico-chemical and biological properties to those of the previously isolated ADase conversion proteins.